Light delivery

ABSTRACT

A light delivery system in a slider includes a channel waveguide, a solid immersion mirror, a near field transducer, and a planar waveguide assembly. The solid immersion mirror focuses light to the near field transducer. In one implementation, the slider includes a first reflective element and a second reflective element formed in the slider to induce an offset between a light source and the near field transducer. The reflective elements redirect light received from a light source between the reflective elements to a focusing element (e.g., a solid immersion mirror) focused on a near field transducer. The reflective elements translate the light in accordance with the offset between the light source and the near field transducer.

SUMMARY

Implementations described and claimed herein provide a light deliverysystem in a slider including a channel waveguide, a solid immersionmirror, a near field transducer, and a planar waveguide assembly. Thesolid immersion mirror focuses light to the near field transducer. Inone implementation, the slider includes a first reflective element and asecond reflective element formed in the slider to induce an offsetbetween a light source and the near field transducer. The reflectiveelements redirect light received from a light source between thereflective elements to a focusing element (e.g., a solid immersionmirror) focused on a near field transducer. The reflective elementstranslate the light in accordance with the offset between the lightsource and the near field transducer.

Other implementations are also described and recited herein.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 illustrates a data storage device having an example lightdelivery system.

FIG. 2 illustrates an example light delivery system for anear-field-transducer-aligned light source.

FIG. 3 illustrates another example light delivery system for anear-field-transducer-aligned light source.

FIG. 4 illustrates yet another example light delivery system for anear-field-transducer-aligned light source.

FIG. 5 illustrates yet another example light delivery system for anear-field-transducer-aligned light source.

FIG. 6 illustrates an example light delivery system for anear-field-transducer-offset light source.

FIG. 7 illustrates another example light delivery system for anear-field-transducer-offset light source.

FIG. 8 illustrates yet another example light delivery system for anear-field-transducer-offset light source.

FIG. 9 illustrates a thin transparent dielectric layer between awaveguide and a sidewall of a light delivery system.

FIG. 10 illustrates example operations for heating a location on astorage medium by delivering light to an NFT in a slider.

DETAILED DESCRIPTIONS

Implementations of the technology described herein may be employed inthe context of a data storage system, although other applications mayalso be contemplated for light delivery using such technology.

FIG. 1 illustrates a data storage device 100 having an example lightdelivery system, shown in more detail in an exploded view 102. Althoughother implementations are contemplated, in the illustratedimplementation, the data storage device 100 includes a storage medium104 (e.g., a magnetic data storage disc) on which data bits can berecorded using a magnetic write pole and from which data bits can beread using a magnetoresistive element. The storage medium 104 rotatesabout a spindle center or a disc axis of rotation 105 during rotation,and includes an inner diameter 106 and an outer diameter 108 betweenwhich are a number of concentric data tracks 110. It should beunderstood that the described technology may be used with a variety ofstorage formats, including continuous magnetic media, discrete track(DT) media, shingled media, etc.

Information may be written to and read from data bit locations in thedata tracks on the storage medium 104. A transducer head assembly 124 ismounted on an actuator assembly 120 at an end distal to an actuator axisof rotation 122. The transducer head assembly 124 flies in closeproximity above the surface of the storage medium 104 during discrotation. The actuator assembly 120 rotates during a seek operationabout the actuator axis of rotation 122. The seek operation positionsthe transducer head assembly 124 over a target data track for read andwrite operations.

In an implementation employing Heat-Assisted-Magnetic-Recording (HAMR),the recording action is assisted by a heat source applied to a bitlocation on the storage medium 104. The data bits (e.g., user data bits,servo bits, etc.) are stored in very small magnetic grains embeddedwithin layers of the storage medium 104. The data bits are recorded inthe magnetic grains within tracks 110 on the storage medium.

Generally, HAMR technology employs a storage medium (such as the storagemedium 104) having a very high magnetic anisotropy, which contributes tothermal stability of the magnetization of the small magnetic grains inthe storage medium 104. By temporarily heating the storage medium 104during the recording process, the magnetic coercivity of the magneticgrains can be selectively lowered below an applied magnetic write fieldin a tightly focused area of the storage medium 104 that substantiallycorresponds to an individual data bit. The heated region is then rapidlycooled in the presence of the applied magnetic write field, whichencodes the recorded data bit in the heated region based on the polarityof the applied magnetic write field. After cooling, the magneticcoercivity substantially returns to its pre-heating level, therebystabilizing the magnetization for that bit. This write process isrepeated for multiple data bits on the storage medium, and such databits can be read using a magnetoresistive read head.

The exploded view 102 schematically illustrates a cross-sectional viewof the transducer head assembly 124, as seen from a cross-trackperspective. The transducer head assembly 124 is supported by asuspension 126 extending from the arm of the actuator assembly 120. Inthe implementation illustrated in the exploded view 102, the transducerhead assembly 124 includes, among other features, a slider 128, a lightsource 130 (e.g., a laser), and a waveguide 132. An air-bearing surface134 of the slider 128 “flies” across the surface of the storage medium104, reading and writing data bits from and to the magnetic grains inthe surface of the storage medium 104.

The light source 130 directs light into the waveguide 132, which has ahigh contrast in the refractive index between the waveguide core and itscladding. The light propagating through the waveguide 132 is focused byan optical focusing element, such as a planar solid immersion mirror(SIM), into a near-field-transducer (NFT) (not shown). Near field opticsmake use of apertures and/or antennas to cause a thermal increase in adata bit location on the surface of the storage medium 104 (e.g., viasurface plasmon effects). As a result, data bit location on the surfaceis heated, selectively reducing the magnetic coercivity of the magneticgrains at the data bit location, relative to other areas of the surface.Accordingly, a magnetic field applied to the heated data bit location(as it cools) is sufficient to record a data bit at the location withoutdisturbing data bits in adjacent, non-heated bit locations. In oneimplementation, the magnetic field is supplied to a write pole in thetransducer head assembly 124, wherein the write pole is positioned inthe near proximity of the NFT. In this manner, the heating area cansubstantially determine the writable area (e.g., the data bitdimension). There are various methods of launching light into a slider.In one implementation, free space light delivery involves directinglight from free space to a grating coupler fabricated in a slider. Inthe implementation shown in FIG. 1, called laser-on-slider lightdelivery, the laser diode is butt-coupled to the waveguide 132. Yetanother configuration, called laser-in-slider light delivery, alsoemploys butt coupling, although other methods of light delivery may beemployed.

FIG. 2 illustrates an example light delivery system 200 for anear-field-transducer-aligned light source (such as a laser diode 202).As shown, the laser diode 202 is affixed on the slider 204, which is inproximity to a storage medium 205. Light emitted from the laser diode202 is coupled into a channel waveguide 206 by a waveguide inputcoupler, propagated through a planar waveguide 207, and focused by a SIM208 to an NFT 210. The NFT 210 causes heating at a bit location 220 inthe storage medium 205 (e.g., via surface plasmon effects). As shown inFIG. 2, the light-emitting output of the laser diode 202 issubstantially aligned with the channel waveguide 206 and the NFT 210along a single axis. In one implementation, the planar waveguide 207 andthe SIM 208 are formed in a “planar waveguide assembly.”

(X,Y) represent a right-handed Cartesian coordinate system, with thecoordinate origin (x,y)=(0,0) at geometric focal point of the SIM.Although various shapes may be employed, in one implementation, theshape of the SIM 208 is elliptical and represented by

$\begin{matrix}{{{\frac{c^{2}}{c^{2} - h^{2}}x^{2}} + \left( {y - \frac{h}{2}} \right)^{2}} = \frac{c^{2}}{4}} & {1(a)} \\{c = {\sqrt{\left( \frac{w_{b}}{2} \right)^{2} + h^{2}} + \frac{w_{b}}{2}}} & {1(b)}\end{matrix}$

where h represents the distance along the Y axis from the exit of thechannel waveguide 206 to the SIM focal plan 212, c represents theoptical path length, normalized by the effective mode index of theplanar waveguide 207, and w_(b) represents the SIM bottom width at theSIM focal plane 212, as shown in FIG. 2. In some implementations, w_(b)is typically a few microns while the NFT width is typically smaller thana micron, although other dimensions and dimensional ratios may beemployed.

As an example, given a μPemto slider format of 700 μm×180 μm×850 μm anda waveguide input coupler of 100 μm in length, an h=80 μm may beemployed. The light beam exiting the channel waveguide 206 is divergent,with a maximum half angular width of θ_(max). For light deliveryefficiency, the optical rays at θ_(max) from the channel waveguidearrive at the rim of the top of the SIM 208 opening. The SIM collectionefficiency and the range of angles of incidence on the SIM 208 arehigher at lower values of θ_(max), which can be achieved with a wideroutput channel at the exit of the channel waveguide 206.

The maximum available channel waveguide width is limited by the cut-offof the first higher mode of the channel waveguide 206, and the optimalchannel output end width is determined based on light deliveryefficiency to the NFT 310 and for NFT excitation efficiency. Assuming a150-nm thick Ta₂O₅ channel waveguide of refractive index n=2.09 withAl₂O₃ cladding layers (n=1.65), the maximum channel width for thefundamental transverse-electric (TE) mode cut-off may be computed to <1μm. At a channel width=1 μm, θ_(max)=25.7°, which yields 67% SIMcollection efficiency. If π-phase difference in the wave front of theleft half of incident light beam from the right half of the incidentbeam is desired, a left-right (e.g., laterally) asymmetric SIM may beemployed, such that the optical path from left and right optical rayshas a π-phase difference.

FIG. 3 illustrates another example light delivery system 300 for anear-field-transducer-aligned light source (such as a laser diode 302).As shown, the laser diode 302 is mounted on the slider 304, which is inproximity to a storage medium 305. Light emitted from the laser diode302 is coupled into a channel waveguide 306 by a waveguide inputcoupler, propagated through a planar waveguide 307, and focused by a SIM308 to an NFT 310. The NFT 310 causes heating at a bit location 320 inthe storage medium 305 (e.g., via surface plasmon effects). As shown inFIG. 3, the light-emitting output of the laser diode 302 issubstantially aligned with the channel waveguide 306 and the NFT 310along a single axis. In one implementation, the planar waveguide 307 andthe SIM 308 are formed in a “planar waveguide assembly.”

(X,Y) represent a right-handed Cartesian coordinate system, with thecoordinate origin (x,y)=(0,0) at geometric focal point of the SIM.Although various shapes may be employed, in one implementation, theshape of the SIM 308 is elliptical and represented by Equations 1(a) and1(b). If π-phase difference in the wave front of the left half ofincident light beam from the right half of the incident beam is desired,a left-right (e.g., laterally) asymmetric SIM may be employed, such thatthe optical path from left and right optical rays has a π-phasedifference.

The width of the channel waveguide 306 is smaller than the width of thechannel waveguide 206 shown in the implementation of FIG. 2. Thenarrower channel waveguide 306 improves input coupling efficiency. Tofurther improve light delivery to the NFT 310, a beam expander 312 isattached at the end of the channel waveguide 306, which suppresses theoccurrence of high order modes and decreases θ_(max). In one example,θ_(max)=15°, w_(b)=4.5 μm, and h=60 μm, yielding a 78% SIM collectionefficiency.

FIG. 4 illustrates yet another example light delivery system 400 for anear-field-transducer-aligned light source (such as a laser diode 402).As shown, the laser diode 402 is mounted on the slider 404, which is inproximity to a storage medium 405. Light emitted from the laser diode402 is coupled into a channel waveguide 406 by a waveguide inputcoupler, propagated through a planar waveguide 407, and focused by a SIM408 to an NFT 410. The NFT 410 causes heating at a bit location 420 inthe storage medium 405 (e.g., via surface plasmon effects). As shown inFIG. 4, the light-emitting output of the laser diode 402 issubstantially aligned with the channel waveguide 406 and the NFT 410along a single axis. (X,Y) represent a right-handed Cartesian coordinatesystem, with the coordinate origin (x,y)=(0,0) at geometric focal pointof the SIM. In the illustrated implementation, two reflective elements412 are placed at the sides of the bottom of the SIM 408. In oneimplementation, the planar waveguide 407, the SIM 408, and thereflective elements 412 are formed in a “planar waveguide assembly.”

Although various shapes may be employed, in one implementation, theshape of the SIM 408 can be represented as follows, where t representsthe thickness of the reflective elements 412:

$\begin{matrix}{x = \frac{4{h\left( {h - t} \right)}\sin \; \theta}{\left( {{3h} - {2t}} \right) - {\left( {h - {2t}} \right)\cos \; \theta}}} & {2(a)} \\{y = {\frac{4{h\left( {h - t} \right)}\cos \; \theta}{\left( {{3h} - {2t}} \right) - {\left( {h - {2t}} \right)\cos \; \theta}} - \left( {h - {2t}} \right)}} & {2(b)}\end{matrix}$

FIG. 5 illustrates yet another example light delivery system 500 for anear-field-transducer-aligned light source (such as a laser diode 502).As shown, the laser diode 502 is mounted on the slider 504, which is inproximity to a storage medium 505. Light emitted from the laser diode502 is coupled into a channel waveguide 506 by a waveguide inputcoupler, propagated through a planar waveguide 507, and focused by a SIM508 to an NFT 510. The NFT 510 causes heating at a bit location 520 inthe storage medium 505 (e.g., via surface plasmon effects). As shown inFIG. 5, the light-emitting output of the laser diode 502 issubstantially aligned with the channel waveguide 506 and the NFT 510along a single axis.

(X,Y) represent a right-handed Cartesian coordinate system, with thecoordinate origin (x,y)=(0,0) at geometric focal point of the SIM. Inthe illustrated implementation, a second reflective element 512 isplaced at the sides of the geometric focal points of the SIM 508. In oneimplementation, the planar waveguide 507, the SIM 508, and thereflective element 512 are formed in a “planar waveguide assembly.”Although various shapes may be employed, in one implementation, theshape of the SIM 508 can be represented by Equations 2(a) and 2(b). Ifπ-phase in the wave front of the left side of incident light beam fromthe right side of the incident beam is desired, a left-right (e.g.,laterally) asymmetric SIM 508 may be employed, such that the opticalpath from left and right optical rays has a π-phase difference.

FIG. 6 illustrates an example light delivery system 600 for anear-field-transducer-offset light source (such as a laser diode 602).As shown, the laser diode 602 is mounted on the slider 604, which is inproximity to a storage medium 605. Light emitted from the laser diode602 is coupled into a channel waveguide 606 by a waveguide input coupler(e.g., via butt coupling) along a first axis of the slider 604,propagated through a planar waveguide 607, and focused by a SIM 608 toan NFT 610 along a second axis of the slider 604. To improve theposition alignment tolerance between the channel waveguide 606 and therest of the optical system, and to shape the light beam, a beam expander612 is attached at the end of the channel waveguide 606, whichsuppresses the occurrence of high order modes and decreases θ_(max). TheNFT 610 causes heating at a bit location 620 in the storage medium 605(e.g., via surface plasmon effects).

In contrast to the implementations shown in FIGS. 2, 3, 4, and 5, theimplementation shown in FIG. 6 introduces an offset 601 (e.g., 100 μm)between the axis 631 of the laser diode 602 and the axis 630 of the NFT610. Such an offset 601 can make room on the top of the slider 604 forother features, such as a bonding pad 603. The offset 601 also filtersout most of the light that is not coupled into the channel waveguide 606from the laser diode 602, which eases the assembly of the laser diodesubmount onto the slider 604. In the illustrated implementation, tworeflector elements 622 and 624 may be employed to accommodate the offset601, directing the optical rays from the offset laser diode 602 to theNFT 610 located substantially in the center of the slider 604. It shouldbe understood that such offsetting configurations need not be limited touse with a slider-centered NFT. The reflective element 622 may be flat,concave, convex, or otherwise configured to yield a desired size oflight beam incident on the SIM 608. The reflective element 624 performsas a collimating element to collimate the light beam into the SIM 608.Although various shapes may be employed, in one implementation, theshape of the SIM 608 substantially parabolic.

As an example, given a slider format of 700 μm×180 μm×850 μm, awaveguide input coupler of 100 μm in length, and beam expander of ˜50 μmin length, the beam exiting from the channel waveguide 606 and beamexpander 612 is divergent, with a maximum half angular width θ_(max).The reflective element 622 is the light delivery system 600 is adistance of x₀ from the end of the beam expander 612 and shown as flat,resulting in a beam size on the SIM 608 of ˜50 μm. The distance from thereflective element 622 to the SIM focal plane 611 is designated as H₁and that of the reflective element 624 is designated as H₂. H_(S)represents the height of the SIM 608 as measured from the SIM focalplane 611. (X,Y) represents a right-handed Cartesian coordinate system,with the coordinate origin (x,y)=(0,0) at the output of the channelwaveguide 606 and beam expander 612, with the X-axis aligned with thechannel waveguide 606. In one implementation, the planar waveguide 607,the SIM 608, and the reflective elements 622 and 624 are formed in a“planar waveguide assembly.”

The reflective element 622 is shown as flat, rotated counterclockwisefrom the X axis by θ_(max)/2, and located at a distance of x₀ from theend of the beam expander 612. The reflective element 622 reflects thecentral ray existing from the beam expander 612 at an angle θ₀, asdetermined by the offset 601 and the relative distance between thereflective elements 622 and 624:

$\theta_{0} = {\tan^{- 1}\left( \frac{offset}{H_{2} - H_{1}} \right)}$

In one example, H₂=180 μm, H₁=48 μm, offset=102 μm, and θ₀=37.694°.

The beam divergent angle from the beam expander (i.e., θ_(max)) issmall, so Gaussian beam approximation can be used to trace the lightbeam propagating between the reflective elements 622 and 624. Infirst-order Gaussian optics, beam reflections from a flat mirror (e.g.,the reflective element 622) may be modeled by placing a virtual sourcelocated at (x_(v),y_(v)) behind the mirror in the (X,Y) coordinatesystem:

x _(v) =x ₀[1+cos(θ₀)]  3(a)

y _(v) =x ₀ sin(θ₀)  3(b)

The reflective element 624 is a canted parabolic collimator. To preventlight loss in the central gap of the SIM 608, a canted collimator may beemployed to direct the light into the two SIM sidewalls, as shown inFIG. 6. The reflective element 624 may also have a split, Δx, as shownin FIG. 6, to introduce a phase shift between the two split beams to theSIM sidewalls. For example, if a π-phase difference is desired,

${\Delta \; x} = {0.5\frac{\lambda}{n_{eff}}}$

where λ represents the light wavelength in a vacuum and n_(eff)represents the effective mode index of the planar waveguide. (X′,Y′)represents another a right-handed Cartesian coordinate system, with thecoordinate origin (x,y)=(0,0) at (x_(v),y_(v)). The X′ axis is parallelto the central ray reflected from the reflective element 622. Thetransformation between the (X,Y) coordinate system and the (X′,Y′)coordinate system is shown by:

$\begin{pmatrix}x^{\prime} \\y^{\prime}\end{pmatrix} = {\begin{pmatrix}{{- \cos}\; \theta_{0}} & {{- \sin}\; \theta_{0}} \\{{- \sin}\; \theta_{0}} & {\cos \; \theta_{0}}\end{pmatrix}\begin{pmatrix}{x - x_{v}} \\{y - y_{v}}\end{pmatrix}}$ $\begin{pmatrix}{x - x_{v}} \\{y - y_{v}}\end{pmatrix} = {\begin{pmatrix}{{- \cos}\; \theta_{0}} & {{- \sin}\; \theta_{0}} \\{{- \sin}\; \theta_{0}} & {\cos \; \theta_{0}}\end{pmatrix}\begin{pmatrix}x^{\prime} \\y^{\prime}\end{pmatrix}}$

An optical ray exiting from the beam expander 612 at an angle of θintersects the reflective element 622 at (x₁,y₁), the reflective element624 at (x₂,y₂), and the SIM 608 at (x,y):

$x_{1} = \frac{x_{0}}{1 + {{\tan (\theta)}{\tan \left( \frac{\theta_{0}}{2} \right)}}}$y₁ = x tan (θ)$x_{2}^{\prime} = {{{\frac{x_{02}^{\prime}{\cos (\theta)}}{\cos^{2}\left( {\theta + \theta_{2}} \right)}\left\lbrack {1 - {\sin \left( {\theta + \theta_{2}} \right)}} \right\rbrack}y_{2}^{\prime}} = {{x\; {\tan (\theta)}{where}x_{02}^{\prime}} = {{\left\lbrack {1 + {\sin \left( \theta_{2} \right)}} \right\rbrack x_{02}\theta_{2}} = {{\frac{\pi}{2} - {\theta_{1}x_{02}}} = \left\{ {{\begin{matrix}{x_{02p} - {0.5\Delta \; x\mspace{14mu} {for}\mspace{14mu} {the}\mspace{14mu} {upper}\mspace{14mu} {sector}}} \\{x_{02p} + {0.5\Delta \; x\mspace{14mu} {for}\mspace{14mu} {the}\mspace{14mu} {lower}\mspace{14mu} {sector}}}\end{matrix}x_{02p}} = {{\sqrt{({offset})^{2} + \left( {H_{2} - H_{1}} \right)^{2}} + {x_{0}\theta_{1}}} = \left\{ {{\begin{matrix}{\theta_{0} - {\Delta \; \theta \mspace{14mu} {for}\mspace{14mu} {the}\mspace{14mu} {upper}\mspace{14mu} {sector}}} \\{\theta_{0} + {\Delta \; \theta \mspace{14mu} {for}\mspace{14mu} {the}\mspace{14mu} {upper}\mspace{14mu} {sector}}}\end{matrix}{\Delta\theta}_{0}} = {{{\tan \left( \frac{0.5w_{b}}{H_{2}} \right)}x^{\prime}} = {{x_{f}^{\prime} + {{\sin \left( \theta_{2} \right)}\begin{Bmatrix}{{\left( {x_{2}^{\prime} - x_{f}^{\prime}} \right){\cos \left( \theta_{2} \right)}{\cot \left( \theta_{2} \right)}} -} \\{{\left( {y_{2}^{\prime} - y_{f}^{\prime}} \right)\cos \; \theta_{2}} -} \\{\frac{x_{03}^{\prime}}{2} + {\frac{1}{2x_{03}^{\prime}}\begin{bmatrix}{{\left( {x_{2}^{\prime} - x_{f}^{\prime}} \right)\cos \; \theta_{2}} -} \\{\left( {y_{2}^{\prime} - y_{f}^{\prime}} \right)\sin \; \theta_{2}}\end{bmatrix}}^{2}}\end{Bmatrix}y^{\prime}}} = {{y_{2}^{\prime} + {{\tan \left( \theta_{1} \right)}\left( {x^{\prime} - x_{2}^{\prime}} \right)}} = {{y_{2}^{\prime} + {{\cot \left( \theta_{2} \right)}\left( {x^{\prime} - x_{2}^{\prime}} \right)x_{03}^{\prime}}} = {\frac{{\cos \left( \theta_{2} \right)} - {\frac{y^{\prime}}{x^{\prime}}{\sin \left( \theta_{2} \right)}}}{{\sin \left( \theta_{2} \right)} + {\frac{y^{\prime}}{x^{\prime}}{\cos \left( \theta_{2} \right)}}}\left\lbrack {{\left( {x_{b}^{\prime} - x_{f}^{\prime}} \right){\cos \left( \theta_{2} \right)}} - {\left( {y_{b}^{\prime} - y_{f}^{\prime}} \right){\sin \left( \theta_{2} \right)}}} \right\rbrack}}}}}} \right.}} \right.}}}}$

For the left SIM sidewall:

$\begin{pmatrix}x_{b}^{\prime} \\y_{b}^{\prime}\end{pmatrix} = {\begin{pmatrix}{- {\cos \left( \theta_{0} \right)}} & {- {\sin \left( \theta_{0} \right)}} \\{- {\sin \left( \theta_{0} \right)}} & {\cos \left( \theta_{0} \right)}\end{pmatrix}\begin{pmatrix}{x_{f} - x_{v}} \\{y_{f} - {0.5w_{b}} - y_{v}}\end{pmatrix}}$$\frac{y^{\prime}}{x^{\prime}} = {- {\cot \left( {\theta_{0} + \frac{\Delta \; \theta_{0}}{2} + \frac{\pi}{4}} \right)}}$

For the right SIM sidewall:

$\begin{pmatrix}x_{b}^{\prime} \\y_{b}^{\prime}\end{pmatrix} = {\begin{pmatrix}{- {\cos \left( \theta_{0} \right)}} & {- {\sin \left( \theta_{0} \right)}} \\{- {\sin \left( \theta_{0} \right)}} & {\cos \left( \theta_{0} \right)}\end{pmatrix}\begin{pmatrix}{x_{f} - x_{v}} \\{y_{f} + {0.5w_{b}} - y_{v}}\end{pmatrix}}$$\frac{y^{\prime}}{x^{\prime}} = {- {\cot \left( {\theta_{0} - \frac{\Delta \; \theta_{0}}{2} - \frac{\pi}{4}} \right)}}$

Based on the foregoing, (x₂′, y₂′) and (x′,y′) represent the rayintersection at the reflective element 624 and the ray intersection atthe SIM 608 in the local coordinate system, respectively. Likewise,(x_(f)′, y_(f)′) represents the coordinates of the SIM focal point inthe local coordinate system, and w_(b) represents the width of thebottom opening of the SIM 608 at the focal plane.

FIG. 7 illustrates another example light delivery system 700 for anear-field-transducer-offset light source (such as a laser diode 702).As shown, the laser diode 702 is mounted on the slider 704, which is inproximity to a storage medium 705. Light emitted from the laser diode702 is coupled into a channel waveguide 706 by a waveguide inputcoupler, expanded by a beam expander 712, propagated through a planarwaveguide 707, and focused by a canted SIM 708 to an NFT 710. The NFT710 causes heating at a bit location 720 in the storage medium 705(e.g., via surface plasmon effects).

In contrast to the implementations shown in FIGS. 2, 3, 4, and 5, theimplementation shown in FIG. 7 introduces an offset 701 (e.g., 100 μm)between the laser diode 702 coupled channel waveguide 706 and the NFT710. Such an offset 701 can make room on the top of the slider 704 forother features, such as a bonding pad 703. In the illustratedimplementation, two reflector elements 722 and 724 may be employed toaccommodate the offset 701 between the axis 731 of the laser diode 702and the axis 730 of the NFT 710, directing the optical rays from theoffset laser diode 702 to the NFT 710 located substantially in thecenter of the slider 704. It should be understood that such offsettingconfigurations need not be limited to use with a slider-centered NFT.The reflective element 722 may be flat, concave, convex, or otherwiseconfigured to yield a desired size of light beam incident on the SIM708. The reflective element 724 performs as a canted collimating elementto collimate the light beam into the SIM 708. Although various shapesmay be employed, in one implementation, the shape of the SIM 708 issubstantially parabolic. In one implementation, the planar waveguide707, the SIM 708, and the reflective elements 722 and 724 are formed ina “planar waveguide assembly.”

In contrast to the collimating reflective element 624 of FIG. 6, thereflecting element 724 in FIG. 7 does not include a split (e.g., Δx=0).To determine the light beam size on the SIM 708, Gaussian beampropagation may be employed. Assuming the w₀ is the beam radius at its1/e amplitude point at the exit of the beam expander 712, the Rayleighlength,

$z_{R} = \frac{\pi \; w_{0}^{2}}{\lambda}$

which corresponds to a distance of propagation to a point where the 1/e²radius of the beam is √{square root over (2)} times that at the beamwaist, or the on-axis intensity of the beam is one-half of that at thebeam waist. The beam waist is at the x₀₂ distance from the reflectiveelement 724. In this manner, the beam size w₁ at the beam waist afterthe reflective element 724 is given by:

$w_{2} = {\frac{x_{02}}{z_{R}}w_{0}}$

FIG. 8 illustrates yet another example light delivery system 800 for anear-field-transducer-offset light source (such as a laser diode 802).As shown, the laser diode 802 is mounted on the slider 804, which is inproximity to a storage medium 805. Light emitted from the laser diode802 is coupled into a channel waveguide 806 by a waveguide inputcoupler, propagated through a planar waveguide 807, and focused by a SIM808 to an NFT 810. To further improve light delivery to the NFT 810 andallow more alignment tolerance between the channel waveguide 806 and therest of the optical elements (e.g., see reflector elements 822 and 824,and the SIM 808), a beam expander 812 is attached at the end of thechannel waveguide 806, which suppresses the occurrence of high ordermodes and decreases θ_(max). The NFT 810 causes heating at a bitlocation 820 in the storage medium 805 (e.g., via surface plasmoneffects).

In contrast to the implementations shown in FIGS. 2, 3, 4, and 5, theimplementation shown in FIG. 8 introduces an offset 801 (e.g., 100 μm)between the laser diode 802 coupled channel waveguide 806 and the NFT810. Such an offset 801 can make room on the top of the slider 804 forother features, such as a bonding pad 803. In the illustratedimplementation, two reflector elements 822 and 824 may be employed toaccommodate the offset 801 between the axis 830 of the laser diode 802and the axis 831 of the NFT 810, directing the optical rays from theoffset laser diode 802 to the NFT 810 located substantially in thecenter of the slider 804. It should be understood that such offsettingconfigurations need not be limited to use with a slider-centered NFT.The reflective element 822 may be flat, concave, convex, or otherwiseconfigured to yield a desired size of light beam incident on the SIM808. The reflective element 824 performs as a collimating element tocollimate the light beam into the SIM 808, but in contrast to thereflective element 724 of FIG. 7, the reflective element 824 and the SIM808 are not canted. Although various shapes may be employed, in oneimplementation, the shape of the SIM 808 is substantially parabolic. Inone implementation, the planar waveguide 807, the SIM 808, and thereflective elements 822 and 824 are formed in a “planar waveguideassembly.”

By removing the cant from both the reflective element 824 and the SIM808, previously presented equations apply by setting

Δθ₀=0

x ₀₃′=0.5w _(b)

In yet another implementation, the reflector element 824 may be split,in a manner similar to the reflective element 624 of FIG. 6, tointroduce π-phase difference between two halves of the beam.

FIG. 9 illustrates a thin transparent dielectric layer 902 between awaveguide 904 and a sidewall 906 of a light delivery system 900. Thedielectric layer 902 has refraction of index greater than the waveguidemode propagation constant, i.e., n>β. The thickness of the dielectriclayer 902 can be analytically determined by maximizing the reflectivitynear the angle of incidence of the rays 908, where a dip in reflectivityoccurs when the dielectric layer is absent. In one example, a dielectriclayer thickness of ˜100 nm at a light wavelength of 830 nm. Similarcharacteristics may apply to other reflective elements (e.g., reflectiveelements 622 and 624 in FIG. 6, reflective elements 722 and 724 in FIG.7, and reflective elements 822 and 824 in FIG. 8).

FIG. 10 illustrates example operations 1000 for heating a location on astorage medium by delivering light to an NFT in a slider. An emittingoperation 1002 emits light from a light source (such as a laser diode).A receiving operation 1004 couples the light into a channel waveguideformed in a slider. A propagation operation 1006 propagates the lightthrough a planar waveguide in the slider.

An offsetting operation 1008 redirects the light between two reflectiveelements in the planar waveguide to accommodate an offset between thelight source and the NFT. Where no offset is desired, the offsettingoperation 1008 may be omitted, such that the light propagates from thechannel waveguide through the planar waveguide to a focusing element,such as a SIM.

A focusing operation 1010 focuses the light to the NFT, such as via aSIM. A heating operation 1012 heats a location on a storage medium usingthe NFT (such as via surface plasmon effects).

It should be understood that a laterally asymmetric SIM may be used inoffset implementations of the described technology, along with variouscombinations of canted, curved, split, and/or angled reflective elementswithin the slider.

The above specification, examples, and data provide a completedescription of the structure and use of exemplary embodiments of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended. Furthermore, structuralfeatures of the different embodiments may be combined in yet anotherembodiment without departing from the recited claims.

1. A slider comprising: a channel waveguide in the slider, the channelwaveguide being configured to receive light from a light sourcepositioned external to the slider; a near field transducer positioned atan air bearing surface of the slider, the near field transducersubstantially aligned along a single axis with a light emitting outputof the light source and the channel waveguide; a planar waveguideassembly in the slider, the planar waveguide assembly being configuredto receive the light from the channel waveguide and to direct the lightto a solid immersion mirror in the planar waveguide assembly, the solidimmersion mirror being configured to focus the light to the near fieldtransducer; and at least one reflective element configured to direct thelight received from the channel waveguide to the near field transducerin combination with the solid immersion mirror.
 2. The slider of claim 1wherein light source is affixed to an exterior surface of the slider,the exterior surface being opposite an air bearing surface of theslider.
 3. The slider of claim 1 wherein the channel waveguide in theslider is configured to receive light from the light emitting output ofthe light source through butt coupling at an exterior surface of theslider.
 4. (canceled)
 5. (canceled)
 6. (canceled)
 7. (canceled) 8.(canceled)
 9. The slider of claim 1 further comprising: a transparentdielectric layer positioned between a surface of the solid immersionmirror and a sidewall external to the solid immersion mirror within theslider.
 10. The slider of claim 1 further comprising: a beam expanderformed at a light-emitting end of the channel waveguide.
 11. The sliderof claim 1 wherein the solid immersion mirror is asymmetric to provide aphase difference between right and left optical rays of an optical path.12. A data storage system comprising: a light source positioned on anexterior surface of a slider opposite an air bearing surface of theslider; a channel waveguide in the slider, the channel waveguide beingconfigured to receive light from the light source, wherein the lightsource is aligned with a first axis associated with the channelwaveguide and offset from a second parallel axis associated with a nearfield transducer in the slider at an air bearing surface of the slider;and a planar waveguide assembly in the slider, the planar waveguideassembly being configured to receive the light from the channelwaveguide along the first axis and to direct the light to the near fieldtransducer along the second axis.
 13. The data storage system of claim12 wherein the near field transducer is positioned at a distal end of asolid immersion mirror from the light source.
 14. The data storagesystem of claim 12 wherein the planar waveguide assembly of the slidercomprises: at least one reflective element configured to direct thelight received from the channel waveguide to the near field transducerin combination with a solid immersion mirror.
 15. The data storagesystem of claim 12 wherein the planar waveguide assembly furthercomprises: at least two reflective elements configured to direct thelight received from the channel waveguide on the first axis to the nearfield transducer on the second axis.
 16. The data storage system ofclaim 15 wherein at least one of the at least two reflective elementsincludes a phase-shift-introducing split in the light.
 17. The datastorage system of claim 15 wherein at least one of the at least tworeflective elements is configured to collimate the light directed to asolid immersion mirror.
 18. The data storage system of claim 12 whereinthe planar waveguide assembly further comprises a transparent dielectriclayer positioned between a surface of a solid immersion mirror and asidewall external to the solid immersion mirror within the slider. 19.The data storage system of claim 12 further comprising: a beam expanderformed at a light-emitting end of the channel waveguide.
 20. The datastorage system of claim 12 wherein the planar waveguide assemblycomprises a solid immersion mirror in the slider that is laterallyasymmetric to provide a phase difference between right and left opticalrays of an optical path.
 21. The data storage system of claim 12,wherein the light is directed to a solid immersion mirror that issubstantially parabolic.
 22. The slider of claim 1, wherein the at leastone reflective element is concave.
 23. The slider of claim 1, whereinthe at least one reflective element is substantially flat.